1. Field of the Invention
The present invention is related to a thermostat abnormal state detecting apparatus for detecting as to whether or not an abnormal state of a thermostat occurs, which controls temperatures of cooling water of an engine.
2. Description of the Related Art
If engines whose temperatures become high are not caused to be cooled and vehicles are continuously driven for a long time duration, then these engines are brought into overheat conditions. Thus, there is such a risk that the vehicles cannot be completely driven under normal condition. As a consequence, in order to continue the normal drive operations, the temperatures of these engines must be sufficiently cooled. However, when the engines are excessively cooled, gasoline contained in mixed gas cannot be sufficiently vaporized, and thus, combustion conditions are deteriorated, which may cause harmful gas such as hydrocarbon (abbreviated as “HC”) and carbon monoxide (abbreviated as “CO”) to be increased, and also may cause environmental deteriorations. As a result, cooling apparatus capable of maintaining engines of vehicles at proper temperatures are installed on these engines.
FIG. 7 is a diagram for indicating a simplified arrangement of a conventional cooling apparatus 30. The cooling apparatus 30 is arranged by containing a radiator 31, a cooling fan 32, a thermostat 33, a water pump 34, a cooling water circulating path 35, and a pipe path 36. It should be noted that arrows shown in this drawing indicate directions along which cooling water flow. The radiator 31 corresponds to an apparatus for cooling the cooling water. The cooling fan 32 blows wind with respect to the radiator 31 so as to emphasize cooling effects of the cooling water contained in the radiator 31. The thermostat 33 switches operations as to whether or not the cooling water derived from the radiator 31 may be supplied to an engine 37 of a vehicle in response to temperatures. The water pump 34 circulates the cooling water.
When the engine 37 is started, since the temperature of the cooling water contained in the engine 37 is cold, the valve of the thermostat 33 is closed, so that the cooling water does not flow into the radiator 31, but is circulated through the bypass path 36, and is returned to the engine 37 by the water pump 34. Also, when the temperature of the cooling water is increased up to a predetermined valve opening temperature of the thermostat 33 while the vehicle is traveled, the valve of this thermostat 33 is opened, so that the cooling water which is located on the side of the engine 37 and has been heated passes through the cooling water circulating path 35 communicated between the engine 37 and the radiator 31, and then is entered into the radiator 31. When the cooling fan 32 is provided at a position opposite to the radiator 31, the cooling water contained in the radiator 31 is radiated to be cooled by wind blown from the cooling fan 32. The cooled cooling water contained in the radiator 31 is returned via the cooling water circulating path 35 to the engine 37 by the water pump 34. As previously explained, the high temperature of the engine 37 may be cooled to the proper temperature by the cooling apparatus 30.
However, when the engine 37 is driven under warming-up operation after this engine 37 has been started, in such a case that the thermostat 33 is brought into an abnormal state and thus such a condition that the valve of this thermostat 33 is kept opened and is not closed is continued, the cooling water which is circulated in the cooling water circulating path 35 is cooled by the radiator 31. As a result, the time required that the temperature of this cooling water is reached to the proper temperature is delayed, and therefore, a lengthy time period is required until the engine 37 is warmed. As a consequence, when the above-described abnormal state happens to occur in the thermostat 33, this abnormal state must be immediately detected and a warning sign must be indicated to a vehicle driver.
A first conventional radiator malfunction sensing apparatus for sensing an abnormal state of a thermostat calculates a predicted water temperature based upon a thermal load parameter which is correlative to an increase of water temperatures and a water temperature when an engine is started, and also detects an actual water temperature. Both in the case that the predicted water temperature is reached to a predetermined malfunction judging value and the detected actual water temperature is not reached to a predetermined normal state judging value, this radiator malfunction sensing apparatus judges that the thermostat of the radiator is brought into a malfunction state (see, for example, JP-A-2000-8853).
A second conventional vehicle-oriented electronic control apparatus judges as to whether or not an abnormal state of a thermostat based upon a temperature change in cooling water of an engine only just after the engine whose temperature is cold is started. Concretely speaking, if a valve opening failure happens to occur under which a valve of the thermostat is kept opened, then the cooling water is circulated even when the engine whose temperature is cold is started, so that temperature increasing of the cooling water contained in the engine is disturbed. As a consequence, in the second conventional electronic control apparatus, a gradient indicative of an increasing degree of the cooling water temperatures is detected, and since this detected gradient is compared with a gradient of a cooling water temperature under normal operation, this electronic control apparatus judges as to whether or not the valve opening failure of the thermostat happens to occur (see, for example, JP-A-2000-274300).
In the first and second prior art, since the abnormal state detecting process operations for the thermostat are carried out from the ordinary temperature state, or from the lower temperature state than the ordinary temperature state, the abnormal states of the thermostats can be detected. However, in the first and second prior art, even when the abnormal state detecting process operation as to the thermostat is carried out from a semiwarming-up state whose temperature is higher than the ordinary temperature, increasing time of the cooling water temperature which requires that the engine state becomes the warming-up state from the semiwarming-up state is shorter than such an increasing time of the cooling water temperature which requires that the engine state becomes the warming-up state from the starting state, so that the characteristic indicative of the abnormal state of the thermostat cannot be completely grasped. As a consequence, the first and second prior art own such a problem that the abnormal states of the thermostats can be hardly detected from the semiwarming-up states.